Animal development depends on the successive refinement of cell fates and cell potentials. Embryonic stem cells, for example, are pluripotent but their descendents gradually take on more specific fates depending on the extracellular cues they perceive and intrinsic factors they express. Understanding this process at a mechanistic level is important for eventually harnessing the potential of stem cells for medicine, as well as for understanding many diseases, such as cancers, where this process fails to be properly regulated. In this project, the model system to be investigated is appendage specification in the fruit fly, Drosophila melanogaster. One goal is to understand, at a molecular level, how the initial leg and wing primordia become established in the early embryo. A second goal is to characterize the mechanism by which cis-regulatory enhancer elements integrate signaling and transcription factor inputs during the formation of the proximal- distal axis in the leg. A third goal is to investigate how the Epidermal Growth Factor pathway establishes positional information in the distal-most segments of the leg. Together, these Aims will provide significant insights into how appendages are first specified to how final positional information in the leg is achieved.